Rainbow Falls is the highest

waterfall A waterfall is any point in a river or stream where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where meltwater drops over the edge of a tabular iceberg or ice shelf. Waterfalls can be formed in seve ...

on the Middle Fork of the

San Joaquin River The San Joaquin River ( ; ) is the longest river of Central California. The long river starts in the high Sierra Nevada and flows through the rich agricultural region of the northern San Joaquin Valley before reaching Suisun Bay, San Francis ...

, in the eastern

Sierra Nevada The Sierra Nevada ( ) is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primari ...

mountains of

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

, in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

. Plunging to the turbulent water below, the falls are named for the rainbows that appear in their mist on sunny summer days. Rainbow Falls is located within the boundaries of

Devils Postpile National Monument A devil is the personification of evil as it is conceived in many and various cultures and religious traditions. Devil or Devils may also refer to: * Satan * Devil in Christianity * Demon * Folk devil Art, entertainment, and media Film and ...

. About 75,000 years ago,

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

erupted from a vent just east of the present-day falls. The eruption occurred in two stages. The first pulse of lava flowed about westward and pooled in the Middle Fork of the San Joaquin drainage. The second pulse of lava insulated the first, allowing it to cool slowly and to

fracture Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...

vertically. The layer above cooled under different conditions and fractured horizontally. Geologists describe these rocks as platy

rhyodacite Rhyodacite is a volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of those plutonic rocks that are intermediate in composition between monzogranite and granodiorite. Rhyodacites form from rapid ...

; they are visible in the cliffs that surround Rainbow Falls. As water rushes over the cliff, it erodes the vertically fractured rhyodacite more easily. A small

cavern Caves or caverns are natural voids under the Earth's surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance underground (such as rock sh ...

begins to form at the base of the falls, and the overlying rock loses its support and collapses. This process, known as undercutting, causes the waterfall to recede slowly upstream. To date Rainbow Falls has retreated about due to undercutting.

References

{{reflist Landforms of Madera County, California Waterfalls of California Plunge waterfalls

See also

References